1. Field of the Invention
The present invention relates to a non-contact IC card and, more particularly, to a non-contact IC card which prevents radio interference and effectively performs a communication process.
2. Description of the Related Art
Of various types of IC cards, a non-contact type IC card has been utilized in recent years which employs electromagnetic waves, light or the like to exchange signals. FIG. 10 shows tile structure of such a non-contact IC card. A ROM 2 and a RAM 3 are connected through a bus 8 to a CPU 1 controlling the operation of an IC card 1A. An input/output control circuit 4 (hereinafter referred to as an I/O control circuit 4) is connected to the bus 8, which I/O control circuit 4 is used for controlling the output of data to an external unit 9 of an application system and the input of data from it. An antenna 6 is connected to the I/O control circuit 4 via a modulating/demodulating circuit 5. The IC card has a built-in battery 7 which supplies electricity to electric circuits.
In such an IC card 1A, when the antenna 6 receives a request signal in the form of an electromagnetic wave from the external unit 9, the request signal is input through the I/O control circuit 4 to the CPU 1 after having been demodulated by the modulating/demodulating circuit 5. Upon receiving the request signal, the CPU 1 reads the identification information of the IC card 1 which has already been recorded in the RAM 3 and then unconditionally outputs this information in the form of a response signal. The response signal is input via the I/C control circuit 4 to the modulating/demodulating circuit 5, which modulates it before it is transmitted through the antenna 6 to the external unit 9.
There is a type of IC card in which, when it is used, additional data, such as a period, a section and an amount of money, is recorded in a RAM, and, the additional data, together with the response signal, is unconditionally transmitted to an external unit.
The IC card 1A unconditionally transmits the response signal in response to the request signal from the external unit 9. Therefore, when the IC card 1A is placed within an area accessible to the external unit of another non-contact IC card system which has an electrical function similar to that of the external unit 9, the IC card 1A may transmit the response signal to the external unit of the other application system. When a card user simultaneously has two types of non-contact IC cards respectively corresponding to the two different non-contact IC card systems and he passes an area accessible to the external unit of one system, the two IC cards may each receive the request signal from the external unit, thus transmitting a response signal. This causes radio interference and data processing to be performed erroneously.
With the above type of IC card in which the additional data, together with the response signal is transmitted unconditionally, a great amount of time is required to complete a communication in response to the external unit, thus increasing electric power consumed when the card holder passes an area accessible to the external unit, and therefore decreasing the life of the built-in battery.